Two-dimensional capillary electrophoresis-thin layer chromatography separations of amino acid enantiomers using electro-filament transfer

Capillary electrophoresis (CE) is coupled to thin-layer chromatography (TLC) to demonstrate a convenient technique for performing two-dimensional microseparations. CE is interfaced with electrospray, which is operated in the electro-filament mode to produce a narrow (ca. 20 μm) liquid filament. The liquid filament deposits spatially focused bands (ca. 200 μm wide) onto a TLC plate. The TLC plate stores the separation from the CE capillary in the first dimension and then serves as the stationary phase for the chiral separation in the second dimension. Mixtures of dansylated (DNS) derivatives of selected amino acids are separated in the first dimension by the micellar electrokinetic chromatography variation of CE. Reversed-phase TLC separates the enantiomers in the second dimension with a mobile phase containing highly concentrated solutions of β-cyclodextrin. The TLC plates are imaged by using laser-induced fluorescence and a charge-coupled device camera. Prior to TLC development, off-column efficiencies of 130,000 to 190,000 plates per meter were obtained. The enantiomers of four DNS amino acids were baseline resolved using two-dimensional separation and a significant enhancement of the peak capacity over one-dimensional separations is demonstrated. © 2000 John Wiley & Sons, Inc. J Micro Sep 12: 419–428, 2000